uh whut? I use 172.5 cranks on one bike and 175 cranks on another bike. I'm pretty average height but have longer legs and shorter torso.
However... I used to wear more baggy pants with a 32" inseam, but recently started going with more fitted pants in a 30" inseam (my actual heel-crotch inseam is around 32" I think). I just checked crank center to saddle on my road bike (the one with 172.5 cranks), with the saddle set by the shop owner when I purchased the bike, and it's right at 30".
I'm going to check to see what the height is on my MTB later - theoretically it should be a touch lower since it has the 175 cranks on it.